1. Field of the Invention
The present invention relates to blends of a polyester resin, such as polybutylene or polyethylene terephthalate, and an impact resistant interpolymer. The resulting blends find utility as a raw material in the fabrication of formed parts.
2. Description of the Prior Art
Thermoplastic polyester resins which are based on the reaction of aliphatic or aromatic dicarboxylic acids and aliphatic or cycloaliphatic diols are tough materials which find principal utility as an injection molding material for the formation of molded parts having good resistance to friction and wear. Various attempts have been made to improve the impact resistance of such materials. For example, in U.S. Pat. No. 3,919,353 to L. Castelnuovo et al. it is suggested that the polyester resin be blended with a crosslinked polymer having a second order transition temperature lower than 0.degree. C. which is grafted with or which contains polar and/or polarizable monomers or groups. Examples of such polymers are polybutadiene, butadiene-styrene copolymers, butadiene-acrylonitrile copolymers, ethylene-propylene rubbers, polyisobutene, and polyisoprene. Examples of polar grafting monomers or polarizable groups include the acrylic and methacrylic esters, vinyl acetate, acrylonitrile, styrene, and the alkyl styrenes.
Various acrylate based multistage interpolymers which differ from the impact resistance additive proposed by Castelnuovo et al. are known. For example, U.S. Pat. No. 3,655,826 to R. P. Fellmann et al. proposes a three-stage interpolymer which is useful as an impact resistance improver for a variety of thermoplastic polymers without naming thermoplastic polyester resins as an example of a suitable substrate resin. Another three-stage interpolymer comprising acrylate, styrene, and acrylonitrile moieties is described in U.S. Pat. No. 3,944,631 to A. J. Yu et al. This interpolymer has been described in the prior art as an impact improvement additive for polycarbonate resins (U.S. Pat. No. 4,148,842), for blends of chlorinated vinyl chloride and vinyl chloride polymers (U.S. Pat. No. 4,160,793), and for vinyl chloride polymers (U.S. Pat. No. 4,168,285).